When documentary filmmaker Kief Davidson was looking for crew members to accompany him to Rwanda and Sudan in February 2012, he warned them up front there was a good chance they might see a child die.

Davidson would be following eight children with rheumatic heart disease from Rwanda to a state-of-the-art hospital just outside Khartoum, the capital of Sudan, for high-risk surgery.

"Open Heart," which has been nominated for an Academy Award in the short documentary category and will be seen on HBO later this year, features Angelique Tuyishimere, a petite, bright-eyed six-year-old daughter of a Rwandan farmer who spent two years in and out of hospitals, her father falling deeper and deeper into debt paying for food, transportation, treatment, and time away from his crops. Another one of the children is Marie Claver, age 17, sick for close to 10 years, her father never far from her side; she's undergone numerous treatments and by early 2012 she had a hole in her aortic valve.

"We made the film because we were outraged by the situation," Davidson told ABC News. He worked with co-producer Cori Shepherd Stern. "Rheumatic heart disease is such a preventable disease, antibiotics are so cheap, and we wanted to bring attention to it. There's so much attention on AIDS and tuberculosis and malaria [in Africa], but very little on rheumatic heart disease."

Before 1960, it was a leading cause of death for children in the U.S. It begins with strep throat, which can lead to rheumatic fever if untreated, causing permanent damage to the heart valves and muscle. Today, with antibiotics, the disease is rare in children in the West, but according to the World Health Organization, 18 million people in Africa are affected by rheumatic fever or heart disease, two thirds between the ages of 5 and 15.

"I was 100 percent convinced that one of these children was going to die," said Davidson, who has a five-year-old son close to Angelique's age. "I was constantly trying to force myself not to become attached to them."

The Salam Center for Cardiac Surgery, 2,500 miles from Rwanda, began taking patients in 2007. Salam is the continent's only state-of-the-art, free-of-charge cardiac hospital, and the film depicts an immaculate facility, its white, navy and steel the epitome of professionalism, its grounds well-tended and a lush green. Salam is run by Emergency, an Italian-based nonprofit that provides medical care to victims of war, land mines, natural disasters and poverty.

Three quarters of Salam's funding comes from private donors, the remaining 25 percent from the Sudanese government.